Mic 2 PC.. Do I need amp or preamp? and what's the difference?

hunted22

Member
2013-02-02 5:04 pm
Hello..

I'd like to record high quality vocal on PC using a dynamic mic. of course connecting the mic directly into the mic input produce poor sound.. I read that I need to get a pre-amp.. I don't exactly know what that is, and I don't comprehend the deference between amp and preamp. and can't I use an amp for the same job?

thanks in advance
 
An amplifier designed to amplify some low-level signal from a transducer (such as a microphone) and bring it to line level is often called a preamplifier, although the term preamplifier may also refer to a box with a bunch of line inputs, a source selector, volume control and possibly other controls and a line output.

What you need is a microphone preamplifier, that is, an amplifier that is designed to handle microphone signals and bring them to line level. That means among other things that it has to be designed for flat voltage gain over the audio band, with noise optimised for a source impedance in the 200 ohm to 600 ohm range, and with adequate headroom.
 
Basically, a preamp is a voltage gain device while an amp is a power gain device.
The nature of the poor sound should suggest what the fix should be. A level that is too low, or an interface issue, would suggest the need for a preamp. Perhaps a microphone preamp connected to the soundcard line-in, bypassing the card's microphone circuitry, is what you need.
Otherwise, it may be something that could be corrected via computer settings.
 

hunted22

Member
2013-02-02 5:04 pm
Thank you all for your responses..
Okay so I have a small amplifier that I use to power up two speakers in my office.. I don't recall its wattage or specs, but it's about one and a half the size of a car radio.. and the speakers are couple of 120w, 10".. Can't I just use an amp like this to amp the mic‘s signal, and feed the output to the PC (instead of the speakers)? .. will the output of an amplifier like this one be too much power, and damage the PC or something?

What I meant by poor sound is that the volume is too low and sound is too weak.. it's like I'm using my headphone mic.
 
Well, you could. It might not make as much improvement as you'd like. You're talking about a power amp, and the output level would probably need to be kept way down, too close to the noise floor, to function as a quality microphone amp. And exceeding the power supply voltages at the PC inputs is definitely not a good thing, but a real possibility. What you need is just a level boost, some voltage gain, a preamp. Just estimating, something in the neighborhood of 10x-20x gain should work.
 
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At the very beginning of this thread, hunted 22 already stated: "of course connecting the mic directly into the mic input produce poor sound.."

I don't know exactly what is meant by "poor sound", but if it is too high noise floor, then a good low-noise microphone preamplifier can certainly help (while a main amp abused as a microphone preamp can not). PC sound cards typically have very noisy microphone inputs, and even if they haven't, the interference from the PC may make them noisy.
 

hunted22

Member
2013-02-02 5:04 pm
Thank you all guys for your input..
Okay I'm ruling out the idea of using the amp for this. The thing is that, at this moment, I really don't want to spend a lot since first of all, for this project, I'm not looking for HD audio recording.. just good to fair recording. as I mentiond, the issue with connecting the mic directly into the PC is the weak signal which leads to a low volume recording. and second of all, although I'm thinking of investing in a preamp in the near future, I don't like to rush into buying anything until I know exactly what I need.

@dheming I actually was looking yesterday for simple circuit that would do the job.. I found a couple.. what do you recommend?
 
Does your mic have balanced or unbalanced output? There are a couple simple circuits on the Elliott Sound Products site:

Simple unbal mic pre: Low Noise Microphone Preamp

Simple bal mic pre: Project 122

Something else to keep in mind is that dynamic mics often require quite a lot of gain. This is where you can run into hiss problems with simple circuits and/or cheap commercial mic preamps like the Rolls MP13, etc. That might not be a problem for you right now, but as soon as you want to start using your recordings for something it can become an issue.

In my home studio I have a Yamaha MG166cx mixer and an older Presonus TUBEPre. Both are budget devices and neither one is the greatest, but they have done me well for years through various situations. Now I'm in the process of removing the weak links in my rig. I'm selling the Presonus, removing the Yamaha from the monitor path and am planning to build some real professional mic preamps. I've got my sights set on the C84 module from Seventh Circle Audio: SCA Main Product Page
 
Jeepers! Talk about floggimg a dead horse!

The PC input is single ended - DC supply for elecret mics on the ring of the minijack. You either wire your mic to tip and sleeve ( 5V power on the ring) and accept what you get, or build / get a preamp, cheap mixer, external soundcard, or something fancier, - whatever you find acceptable in terms of money...... A cheap dodo mixer can be had for less than 100 bucks - ready made...... Sound quality? You get what you pay for - or what you need....
 
Thank you all guys for your input..
Okay I'm ruling out the idea of using the amp for this. The thing is that, at this moment, I really don't want to spend a lot since first of all, for this project, I'm not looking for HD audio recording.. just good to fair recording. as I mentiond, the issue with connecting the mic directly into the PC is the weak signal which leads to a low volume recording. and second of all, although I'm thinking of investing in a preamp in the near future, I don't like to rush into buying anything until I know exactly what I need.

@dheming I actually was looking yesterday for simple circuit that would do the job.. I found a couple.. what do you recommend?

Hi Hunted22,

I'd say that low volume recording is in itself not a problem. With any audio editing programme you can boost the volume as much as you like afterwards. Only if the noise or interference floor is too high, you will hear unacceptable noise or interference after boosting the volume.

Best regards,
Marcel
 

hunted22

Member
2013-02-02 5:04 pm
@MarcelvdG
I don't really know what is the term that you, audioheads, use to describe the sound I got.. I just said low volume to make my point.. I'd say it was empty.. flat.. had no body to it..
Anyway, I of course tried adding gain and improving the sound with software, but I wasn't happy with the result.




@AuroraB I've decided to build my own preamp for now, and buy a good one in the future. but can you explain this sentence little further "you either wire your mic to tip and sleeve ( 5V power on the ring)"

@dheming Man.. a preamp module for as high as $500!.. the whole sound system I have in my office doesn't coast that much.
The mic has an unbalanced output.. I like the Low Noise Microphone Preamp .. seems simple enough. I was gonna comment on the 30v power, but then I found the 12v version.. I wonder if it would perform well.. maybe I should adjust it for 24v power.

 
PC mic connectors are 3-pole.- signal is on tip, gnd on the outermost sleeve.
The ring in-between is 5V power for elecret mics or capsules. :)

EDIT:
This is an an example of a cheap mixer/preamp http://www.maplin.co.uk/3-channel-microphone-mixer-36158
Maplin also have others.....
-or search Ebay or similar for an external USB soundcard with XLR mic inputs....
new ones can be had for 200USD or less, - used should be cheaper....
 
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